LS13209 - One of many functions of an animal appendage, such as a tail or a feather, is to enable or enhance locomotion. In a calm stream of water or air, a flexible tail-like structure attached to a hind end of a body will spontaneously start to flap – similar to the fluttering of a flag attached to a pole – in the same direction as the incoming stream of flow. This may, however, only be true if the tail (or flag) is sufficiently long. Researchers in Italy and Sweden demonstrate on a simple model that if the flexible structure on the body is short, it flaps at an angle of 20-40 degrees either to the right or left of the incoming stream of flow, thus inducing a net force on the body which may move transversely at no additional cost. This discovery reveals how the mere presence of appendages on animals contributes to locomotion via the interaction with the surrounding fluid flow, without any effort whatsoever from the animal. These findings may also become useful in technological applications where it is of interest to generate a side/lift force on a moving body without increasing the drag from the surrounding fluid.
Thursday, September 13, 2012
Effortless motion of an animal via skew tail flapping
LS13209 - One of many functions of an animal appendage, such as a tail or a feather, is to enable or enhance locomotion. In a calm stream of water or air, a flexible tail-like structure attached to a hind end of a body will spontaneously start to flap – similar to the fluttering of a flag attached to a pole – in the same direction as the incoming stream of flow. This may, however, only be true if the tail (or flag) is sufficiently long. Researchers in Italy and Sweden demonstrate on a simple model that if the flexible structure on the body is short, it flaps at an angle of 20-40 degrees either to the right or left of the incoming stream of flow, thus inducing a net force on the body which may move transversely at no additional cost. This discovery reveals how the mere presence of appendages on animals contributes to locomotion via the interaction with the surrounding fluid flow, without any effort whatsoever from the animal. These findings may also become useful in technological applications where it is of interest to generate a side/lift force on a moving body without increasing the drag from the surrounding fluid.
